If you are using sim + device plan means you tied with 24mnths contract. Can check first your contract status, if already end should be no issues for u to terminate unifi air & using again Streamyx line. But if you are still in contract, I think should be a consideration for TM not to penalize u because you want to change the plan of internet.
No worries! get assistance from Live Chat Mobile on your unifi Air status. After MCO u can visit any nearest TMpoint & much easier for u to settle everything.